I think you are going to see more of this as the EPA is making everyone go to non-vented fuel systems or one-way only systems (air in but not out). As pressure builds up in the tank you are going to have problems and even more so on hot day. I hear about this same problem every single year, year in and year out. I see a day when you will have charcoal canisters one every thing not just cars. I know some people that will only fill their trimmers and saws to half a tank in hopes that will give more time until it acts up. Thank you, EPA.